US3002427A - Anamorphotic attachment - Google Patents

Description

Q f ROOM on 3,002,527, T X 51H/ 7 SEARCH X im @QTL/" I Tzooa 0 3 1961 P. scHFTER rs1-A1. 3,002,427 XZ 7% ANAMORPHOTIC ATTACHMENT X XG .35

Filed May 2. 1958 2. 17;. -2

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United States Patent O 3,002,427 ANAMORPHOTIC ATTACHMENT Paul Schfter, Helmstedt, and Kurt Kirchhoff, Hamburg- Lurnp, Germany, assignors to Isco Optische Werke G.m.b.H., Gottingen-Weende, Germany, a limited-liability company of Germany Filed May 2, 1958, Ser. No. 732,590 Claims priority, application Germany June 13, 1957 3 Claims. (Cl. 88-57) Our present invention relates to an optical system comprising a plurality of cylindrical lenses which form an afocal grou similar to a Galilean telescope, with a collective component on the image side and a dispersive component on the object side of the system. Optical systems of this character, with their cylinder axes usually positioned vertically in order to afford image expansion or contraction in a horizontal plane, are frequently used as anamorphotic front attachments for spherical photographic or projection objectives. These latter objectives, especially those used for picture taking, are generally of relatively short focal length and large image angle which necessitates a wide separation between the negative and positive components of an anamorphotic attachment consisting, in the conventional manner, of two or three air-spaced members. This, in turn, leads to an extremely strong curvature of the dispersive cylindrical front lens, with the extremities of this lens projecting unduly far beyond the plane of its vertex so that satisfactory correction of astigmatism, coma and distortion becomes extremely difficult for light rays converging at the upper and lower marginal zones of the projected image. Other, related drawbacks of these known systems are the great physical length and, in the case of wider ield angles, the large lens diameters of the assembly, the considerable amount of glass involved, the weight, bulk and unwieldiness of the assembly, and the diiculty of finding room on conventional equipment to accommodate the attacll'- ment.

The general object of our present invention is to provide an improved optical system of the character set forth which avoids the disadvantages outlined above.

The anamorphotic system which we have devised, and which embodies the present invention, has four air-spaced cylindrical lens members including two negatively refracting front members and two positively refracting rear members. Advantageously, at least one of: the collective rear members (preferably the one nearer the image plane) is a doublet.

An optical system of this description can be built with a field angle of about 60 and with a total physical length amounting to not more than about 60% of the focal length of the final collective member.

Another feature of our invention resides in the positioning of a concave rear face of the second dispersive member so close to a convex front face of the rst collective member that the spacing between the vertices of these faces is a small fraction, not more than of the combined focal length of the two collective rear members together constituting the positive component of the system. This second dispersive member is advantageously a plano-concave lens and, for convenience of manufacture, may be identical in curvature, thickness and material with the first dispersive member immediately preceding it. The radius of curvature of the aforementioned concave face should at the same time be slightly shorter than that of the adjacent convex face so that the air space encompassed between these two faces is in the shape of a positive meniscus. With the rst collective ice member advantageously designed as a plano-convex lens turning its llat face toward the image side of the system, the second collective lens member is preferably a planoconvex or concave-convex doublet turning its face of shorter radius also toward the image side. The two lens elements which are cemented together to form the doublet should have indices of refraction ditering by at least 0.05. Finally, the separation of the two collective members along their median plane should be not less than 8% and not greater than 25% of the focal length of the rearmost, collective member of the system.

By the observation of the dimensional and constitutive relationships just set forth we are able to provide an optical system which is satisfactorily corrected for aberrations, has limited axial and radial dimensions, and does not introduce objectionable vignetting, due to light-ray cutoff at the lens edges, while aording a wide angle of view.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 shows an anamorphotic attachment according to the invention in a sectional view taken in the optically effective plane;

FIG. 2 is a sectional view of the same attachment taken in the optically ineffective plane; and

FIG. 3 is a view similar to FIG. l, showing a modified attachment according to the invention in combination with a basic spherical objective associated therewith.

The anamorphotic system shown in FIGS. l and 2 comprises a plano-concave first cylindrical lens member T1, having radii r1, r, and median thickness d1, which is separated by an air space d2 from a similar plano-concave lens member T3 having radii r3, r4 and thickness d3. These two members together constitute the dispersive component of the attachment. An air space d4, in the shape of a positive meniscus, separates the negatively refracting member T2 from a positively refracting, planoconvex cylindrical lens T3 having radii f5, r6 and thickness d5; an air space d6 separates the member T3 from its mate T4, which is the final member of the group, the two members T3, T4 together constituting the collective cornponent of the attachment. End member T4 is shown as a doublet composed of a negative front lens (radii rq, rg and thickness dq) and, cemented thereto, a positive rear lens (radii rg, r9 and thickness da), its aspect in the view of FIG. l being that of a positive meniscus.

Preferred numerical values for the parameters rl-r, and d1d8 as well as the refractive indices nd of the lenses T1-T4 are given in the following table.

frv=+167. 66 mm.

The system shown in FIGS. 1 and 2 can be utilized as a front attachment for a conventional spherical objective shown at O in FIG. 3. With the basic objective O focused on infinity, focusing adjustment can be carried out by means of a pair of relatively displaceable spherical lenses preceding the anamorphotic attachment. As taught in our co-pending application Ser. No. 638,151, filed February 4, 1957, now abandoned, one of these spherical lenses can be combined with the anamorphotic front member T1 to form a partly cylindrical, partly spherical lens T1'. This lens differs from front member T1 of the preceding embodiment by the replacement of the plane face (radius r1) of the latter with a spherically convex face of radius ris, resulting in an increase in lens thickness from d1 to du. At SL we have shown a spherically effective, plano-concave supplemental lens (radii r1', r2' and thickness dl') which forms an afocal couple with the forward face of lens T1' and whose axial spacing d2' therefrom is adjustable for focusing purposes. As also taught in our aforementioned co-pending application, the front face of lens T1 would be toric rather than spherical if the corresponding face of member T1 had been cylindrical instead of plane.

Representative numerical values of the parameters of the attachment of FIG. 3 are given in the following table, the values of the unprimed radii rz-rg and thicknesses and spacings dz-da being the same as in Table I.

Table II lenses radii thicknesses na and spacings f1' SL l h ical) +49 65 d{=4,50 1.51

n s er p d,= 2. 20 air space n. (spherical) =+52. 22 T1' d1.=15. 99 1. 52

n (cylindrical)=+33. 42

d; =13.85 air space fs =m Ts d: =4. 95 1, 52

n (cylindrical) ==+33.42

di =1. 97 air space n (cylindrlcal)=+38. 24 T; d =14.84 1. 65

da =17.01 air space n (cylindrical)=123. 57 T unan 1) +37L7s d :L80 L73 4 n cy ca r d ==13. 43 1. 56 n (cylindrlca1)=45. 97

d, =1. 50 air space dw.x=93. 54

It will be noted that in each of the illustrated embodiments the total physical length dwm of the system is well below 70% of the focal length fw of lens member T4, being about 50% thereof in the rst case and approximately 60% inthe second.

We claim:

l. An anamorphotic optical system comprising four air-spaced, cylindrically effective lens members having parallel axes of curvature, said lens members including a dispersive plano-concave first member on the object side of the system, a dispersive plano-concave second member following said tirst member, a collective planoconvex third member following said second member and a collective fourth member following said third member on the image side of the system; said rst and second members constituting a first component of said system and said third and fourth members constituting a second component of said system; said first and second members having like median thicknees, plane surfaces directed toward the object side of said system, and concave faces of like curvature directed toward the image side of said system; said third member having a convex face directed toward the object side 'of said system and a plane surface directed toward the image side of said system, the concave face of said second member and said convex face enclosing an air space in the shape of a positive meniscus, the median thickness of said air space being at most equal to substantially 10% of the focal length of said second component; and said fourth member comprising a first lens element and a second lens element cemented to said rst lens element, the indices of refraction of said first and second lens elements differing by at least 0.05, said third and fourth members being separated by an air space ranging between substantially 8% and 25% of the focal length of said fourth member, said fourth member having a distinctly convex face turned toward the image side of the system and a non-convex face of larger radius of curvature averted from said image side.

2. An anamorphotic optical system comprising four air-spaced, cylindrically effective lens members having parallel axes of curvature, said lens members including a dispersive first member on the object side of the system, a dispersive second member following said rst member, a collective third member following said second member and a collective fourth member following said third member on the image side of the system, said third member being separated from said second member by a relatively small axial distance and from said fourth member by a relatively large axial distance, said trst member T1, said second member T3 and said third member T3 being single lenses and said fourth member T4 consisting of two lenses cemented together, the radii rl-rg, the median thicknesses and spacings l1-d8 and the refrac tive indices nd of all of said lenses having numerical values substantially as given in the following table:

3. An anamorphotic optical system comprising four air-spaced, cylindrically effective lens members having parallel axes of curvature, said lens members including a dispersive first member on the object side of the system, a dispersive second member following said rst member, a collective third member following said second mmbl.' 3.11.4 a Collective fourth member following said 5 6 third member on the image side of the system, said third member being separated from said second member by a lenses radii thicknesses mi relatively small axial distance and from said fourth memand Spacings ber by a relatively large axial distance, said first member being provided with a spherically curved convex forward 5 SL n am dlr-L 50 l 51 face; and a spherically effective plano-concave supplef1 (Spherical) =+4965 d mental lens forming an afocal couple with said forward n, (spherical) +52-22 220 ai' space relatively to said lens members, said first member T1', n (cylmdrical)+33'42 ali-13.85 airspace said second member T2 and said third member T 3 being 10 T2 f1 d 4 9 single lenses and said fourth member T4 consisting of n @wml-man .taag 5 1-52 tw o lenses cemented together, theradiifl' and r2' of n (cyundcal) +38 24 d4 *L97 airspace said supplemental lens SL, its axial thickness d1', its T, 5 84 1.65 spacing d3 from said forward face, the radius r1, of said d 17 01 lr forward face, the median thickness d1, of said first mem- 15 r1 (cy1indr1ca1)=i23. 57 a Space -ber' and the remaining radii rz-rg of al1 of said lenses, T. n (cylmdncal) +371 78 i1-L80 1.73 their median thicknesses and spacings dz-da and their red, :13,43 L 56 fractive indices nd all having numerical values substan- "0 (Y11ndr1ca1)45.97 dal 50 au space tially as given in the following table:

References Cited in the file of this patent UNITED STATES PATENTS 1,829,634 Chretien Oct. 27, 1931 1,932,082 Newcomer Oct. 24, 1933 2,720,813 Cox Oct. 18, 1955 2,721,500 Kohler et al. Oct. 25, 1955 2,752,821 Cook July 3, 1956 2,821,110 Cook Ian. 28, 1958 FOREIGN PATENTS Z-4058-IX/42h. Germany Dec. 22. 1955 335,864 Great Britain Oct. 2, 1930 1,082,780 France June 23, 1954

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